The goals of this research are to determine the principles that underlie the interactions of key biological molecules. We will use the methods of x-ray crystallography to determine the three dimensional structures of selected molecules. In order to understand how nucleic acids interact with one another, with water, with drugs and with proteins we will determine the crystal structures of selected defined sequence oligonucleotides including ones that contain mutagenic and carcinogenic modifications. We will also determine the crystal structures of complexes between wildtype and mutant Catabolite Activating Protein (CAP) and selected variants of the consensus DNA sequence. The results of these will be analyzed to understand the biochemical and thermodynamic data that have been collected for this system. Collagen is an important structural protein whose principal structural element is the triple helix. Triple helices are also found in certain parts of globular proteins. We plan to determine the structures of a series of model collagen peptides with the goal of understanding how collagen assembles and interacts with other molecules in its environment.